The banana weevil Cosmopolites sordidus (Germar, 1824) (Coleoptera: Curculionidae) is an important pest of banana, plantain and ensete. The adult weevil is black and measures 10-15 mm. It is free living, though most commonly found between leaf sheaths, in the soil at the base of the mat or associated with crop residues. The weevil is nocturnally active and very susceptible to desiccation. Adults may remain at the same mat for extended periods of time, while only a small proportion will move > 25 m within 6 months. The weevils rarely fly. Dissemination is primarily through infested planting materials and thats why its important to use clean planting material.

Biology and life cycle The banana weevil Cosmopolites sordidus (Germar, 1824) (Coleoptera: Curculionidae) is an important pest of banana, plantain and ensete. The adult weevil is black and measures 10-15 mm. It is free living, though most commonly found between leaf sheaths, in the soil at the base of the mat or associated with crop residues. The weevil is nocturnally active and very susceptible to desiccation. Adults may remain at the same mat for extended periods of time, while only a small proportion will move > 25 m within 6 months. The weevils rarely fly. Dissemination is primarily through infested planting material. The banana weevil is a “k” selected insect with long life span and low fecundity. Many adults live 1 year, while some survive up to 4 years. On moist substrates, the weevil can survive without feeding for several months. The sex ratio is 1:1. Oviposition rates of more than 1 egg/day have been recorded, but, most commonly, oviposition has been estimated at 1 egg/week. The female places its white, oval eggs singly into holes made by the rostrum. Most oviposition is in the leaf sheaths and rhizome surface. Flowered plants and crop residues are favoured stages for oviposition. The emerging larvae preferentially feed in the rhizome, but will also attack the true stem and, occasionally, the pseudostem. The larvae pass through 5-8 instars. Pupation is in naked cells near the surface of the host plant. Developmental rates are temperature dependent. Under tropical conditions, the egg to adult period is 5-7 weeks. Egg development does not occur below 12°C; this threshold may explain why the weevil is rarely encountered above 1600 mas

The vast majority of the bananas currently grown and consumed were not conventionally bred but are selections made over probably thousands of years from naturally occurring hybrids. Cultivated bananas are very nearly sterile and as a consequence are not propagated from seed but rather through vegetative propagation, primarily suckers as well as more recently micropropagated or tissue cultured bananas. These factors, very old selections, near sterility and vegetative propagation, mean that these bananas have not been genetically improved either for resistance or improved quality and are becoming increasing in affected by serious pests and diseases.